Beam failure recovery for sidelink carrier aggregation

Abstract

Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may transmit reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation. The UE may receive a medium access control element (MAC CE) that indicates a beam failure on the primary sidelink carrier, the one or more secondary sidelink carriers, or both. The UE may transmit, in response to receiving the MAC CE, an aperiodic reference signal on the primary sidelink carrier. Numerous other aspects are described.

What is claimed is: 
     
         1 . A user equipment (UE) for wireless communication, comprising:
 a memory;   a transceiver; and   one or more processors, coupled to the transceiver and the memory, configured to:
 transmit, via the transceiver, reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation; 
 receive, via the transceiver, a medium access control element (MAC CE) that indicates a beam failure on the primary sidelink carrier, the one or more secondary sidelink carriers, or both; and 
 transmit, via the transceiver and in response to receiving the MAC CE, an aperiodic reference signal on the primary sidelink carrier. 
   
     
     
         2 . The UE of  claim 1 , wherein the MAC CE indicates the beam failure on the primary sidelink carrier and the one or more secondary sidelink carriers. 
     
     
         3 . The UE of  claim 2 , wherein the one or more processors, to transmit the reference signals, are configured to transmit a first set of reference signals on the primary sidelink carrier and a respective set of reference signals on each of the one or more secondary sidelink carriers. 
     
     
         4 . The UE of  claim 2 , wherein the one or more processors, to receive the MAC CE, are configured to receive the MAC CE on a secondary sidelink carrier of the one or more secondary sidelink carriers. 
     
     
         5 . The UE of  claim 2 , wherein the one or more processors are further configured to receive, via the transceiver, a random access channel (RACH) preamble on the primary sidelink carrier. 
     
     
         6 . The UE of  claim 5 , wherein the one or more processors are further configured to deactivate the one or more secondary sidelink carriers before receiving the RACH preamble. 
     
     
         7 . The UE of  claim 2 , wherein the primary sidelink carrier is associated with a serving cell. 
     
     
         8 . The UE of  claim 2 , wherein the beam failure includes the failure of all beams on the primary sidelink carrier and the one or more secondary sidelink carriers. 
     
     
         9 . The UE of  claim 1 , wherein the MAC CE indicates a beam failure on the primary sidelink carrier. 
     
     
         10 . The UE of  claim 9 , wherein the one or more processors are configured to transmit, on a secondary sidelink carrier of the one or more secondary sidelink carriers, a message to measure the aperiodic reference signal. 
     
     
         11 . The UE of  claim 10 , wherein the one or more processors are configured to:
 receive, via the transceiver, an aperiodic message indicating a measurement result of the aperiodic reference signal; and   transmit, via the transceiver and based at least in part on the measurement result, a switch message to switch a serving cell from the primary sidelink carrier to a secondary sidelink carrier of the one or more secondary sidelink carriers.   
     
     
         12 . A user equipment (UE) for wireless communication, comprising:
 a memory;   a transceiver; and   one or more processors, coupled to the transceiver and the memory, configured to:
 transmit, via the transceiver, reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation; 
 receive, via the transceiver, a first medium access control element (MAC CE) that indicates a failure of a beam on a secondary sidelink carrier of the one or more secondary sidelink carriers; 
 transmit, via the transceiver and in response to receiving the first MAC CE, one or more aperiodic reference signals on other secondary sidelink carriers of the one or more secondary sidelink carriers; 
 receive, via the transceiver, a message indicating one or more beams of the other secondary sidelink carriers that are viable; and 
 transmit, via the transceiver using a second MAC CE on the primary sidelink carrier, a beam switch message based at least in part on the one or more beams that are viable. 
   
     
     
         13 . The UE of  claim 12 , wherein the one or more processors, to transmit the reference signals, are configured to transmit a first set of reference signals on the primary sidelink carrier and a respective set of reference signals on each of the one or more secondary sidelink carriers. 
     
     
         14 . The UE of  claim 12 , wherein the one or more processors are further configured to transmit, via the transceiver on the primary sidelink carrier, a message to measure the one or more aperiodic reference signals. 
     
     
         15 . A user equipment (UE) for wireless communication, comprising:
 a memory;   a transceiver; and   one or more processors, coupled to the transceiver and the memory, configured to:
 receive, via the transceiver, reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation; 
 detect a beam failure based at least in part on measurement of the reference signals; and 
 transmit, via the transceiver, a first aperiodic medium access control control element (MAC CE) that indicates a failure of one or more beams on one or more of the primary sidelink carrier or the one or more secondary sidelink carriers. 
   
     
     
         16 . The UE of  claim 15 , wherein the beam failure is on the primary sidelink carrier and the one or more secondary sidelink carriers. 
     
     
         17 . The UE of  claim 16 , wherein the one or more processors are further configured to:
 receive, via the transceiver, an aperiodic reference signal for a beam failure recovery procedure; and   perform the beam failure recovery procedure for the primary sidelink carrier, wherein the beam failure recovery procedure is a random access channel (RACH) procedure, and wherein the one or more processors are configured to transmit a RACH preamble on the primary sidelink carrier.   
     
     
         18 . The UE of  claim 15 , wherein the one or more processors, to transmit the first aperiodic MAC CE, are configured to transmit the first aperiodic MAC CE on a secondary sidelink carrier of the one or more secondary sidelink carriers. 
     
     
         19 . The UE of  claim 15 , wherein the one or more processors, to detect the beam failure, are configured to detect the beam failure based at least in part on an expiration of a beam failure count timer or detecting the beam failure based at least in part on a beam failure counter reaching a beam failure threshold for all beams. 
     
     
         20 . The UE of  claim 15 , wherein the one or more processors, to receive the reference signals, are configured to receive a first set of reference signals on the primary sidelink carrier and a set of reference signals on each of the one or more secondary sidelink carriers. 
     
     
         21 . The UE of  claim 15 , wherein the beam failure is on a secondary sidelink carrier of the one or more secondary sidelink carriers. 
     
     
         22 . The UE of  claim 21 , wherein the one or more processors are further configured to:
 receive, via the transceiver, an aperiodic reference signal on the secondary sidelink carrier;   receive, via the transceiver on the primary carrier, a message to measure the aperiodic reference signal;   measure the aperiodic reference signal; and   transmit, via the transceiver, the measurement result in a second aperiodic MAC CE on the secondary sidelink carrier.   
     
     
         23 . The UE of  claim 22 , wherein the one or more processors are further configured to:
 receive, via the transceiver, a switch message to switch a serving cell; and   switch the serving cell from beams of the primary sidelink carrier to beams of a secondary sidelink carrier of the one or more secondary sidelink carriers.   
     
     
         24 . The UE of  claim 22 , wherein the one or more processors are further configured to transmit, via the transceiver, a random access channel preamble on the primary sidelink carrier based at least in part on one or more of the measurement result, an unsuccessful beam reselection on the primary sidelink carrier, or an unsuccessful switch of a serving cell. 
     
     
         25 . The UE of  claim 15 , wherein the one or more processors are further configured to:
 receive, via the transceiver on the primary sidelink carrier, a message to measure one or more aperiodic reference signals;   receive, via the transceiver, the one or more aperiodic reference signals on one or more other secondary sidelink carriers;   select one or more beams, of the one or more other secondary sidelink carriers, that are viable based at least in part on measuring the one or more aperiodic reference signals;   transmit, via the transceiver on a secondary sidelink carrier of the one or more other secondary sidelink carriers, a message indicating the one or more beams that are viable;   receive, via the transceiver using a MAC CE, a beam switch message on the primary sidelink carrier; and   switch to viable beams of a secondary sidelink carrier of the one or more other secondary sidelink carriers.   
     
     
         26 . A method of wireless communication performed by a user equipment (UE), comprising:
 transmitting reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation;   receiving a medium access control element (MAC CE) that indicates a beam failure on the primary sidelink carrier, the one or more secondary sidelink carriers, or both; and   transmitting, in response to receiving the MAC CE, an aperiodic reference signal on the primary sidelink carrier.   
     
     
         27 . The method of  claim 26 , wherein the MAC CE indicates the beam failure on the primary sidelink carrier and the one or more secondary sidelink carriers, and wherein receiving the MAC CE includes receiving the MAC CE on a secondary sidelink carrier of the one or more secondary sidelink carriers. 
     
     
         28 . The method of  claim 26 , wherein the MAC CE indicates a beam failure on the primary sidelink carrier, and wherein the method includes transmitting, on a secondary sidelink carrier of the one or more secondary sidelink carriers, a message to measure the aperiodic reference signal. 
     
     
         29 . The method of  claim 28 , further comprising:
 receiving an aperiodic message indicating a measurement result of the aperiodic reference signal; and   transmitting, based at least in part on the measurement result, a switch message to switch a serving cell from the primary sidelink carrier to a secondary sidelink carrier of the one or more secondary sidelink carriers.   
     
     
         30 . A method of wireless communication performed by a user equipment (UE), comprising:
 transmitting reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation;   receiving a first medium access control element (MAC CE) that indicates a failure of a beam on a secondary sidelink carrier of the one or more secondary sidelink carriers;   transmitting, in response to receiving the first MAC CE, one or more aperiodic reference signals on other secondary sidelink carriers of the one or more secondary sidelink carriers;   receiving a message indicating one or more beams of the other secondary sidelink carriers that are viable; and   transmitting, via a second MAC CE on the primary sidelink carrier, a beam switch message based at least in part on the one or more beams that are viable.   
     
     
         31 . The method of  claim 30 , wherein transmitting the reference signals includes transmitting a first set of reference signals on the primary sidelink carrier and a respective set of reference signals on each of the one or more secondary sidelink carriers. 
     
     
         32 . The method of  claim 30 , further comprising transmitting, on the primary sidelink carrier, a message to measure the one or more aperiodic reference signals. 
     
     
         33 . A method of wireless communication performed by a user equipment (UE), comprising:
 receiving reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation;   detecting a beam failure based at least in part on measurement of the reference signals; and   transmitting a first aperiodic medium access control element (MAC CE) that indicates a failure of one or more beams on one or more of the primary sidelink carrier or the one or more secondary sidelink carriers.   
     
     
         34 . The method of  claim 33 , wherein the beam failure is on the primary sidelink carrier and the one or more secondary sidelink carriers, and wherein the method includes:
 receiving an aperiodic reference signal for a beam failure recovery procedure; and   performing the beam failure recovery procedure for the primary sidelink carrier, wherein the beam failure recovery procedure is a random access channel (RACH) procedure, and wherein the method includes transmitting a RACH preamble on the primary sidelink carrier.   
     
     
         35 . The method of  claim 33 , wherein transmitting the first aperiodic MAC CE includes transmitting the first aperiodic MAC CE on a secondary sidelink carrier of the one or more secondary sidelink carriers. 
     
     
         36 . The method of  claim 33 , wherein the beam failure is on a secondary sidelink carrier of the one or more secondary sidelink carriers, and wherein the method includes:
 receiving an aperiodic reference signal on the secondary sidelink carrier;   receiving, on the primary carrier, a message to measure the aperiodic reference signal;   measuring the aperiodic reference signal; and   transmitting the measurement result in a second aperiodic MAC CE on the secondary sidelink carrier.   
     
     
         37 . The method of  claim 33 , further comprising:
 receiving, on the primary sidelink carrier, a message to measure one or more aperiodic reference signals;   receiving the one or more aperiodic reference signals on one or more other secondary sidelink carriers;   selecting one or more beams, of the one or more other secondary sidelink carriers, that are viable based at least in part on measuring the one or more aperiodic reference signals;   transmitting, on a secondary sidelink carrier of the one or more other secondary sidelink carriers, a message indicating the one or more beams that are viable;   receiving, via a MAC CE, a beam switch message on the primary sidelink carrier; and   switching to viable beams of a secondary sidelink carrier of the one or more other secondary sidelink carriers.   
     
     
         38 . An apparatus for wireless communication, comprising:
 means for transmitting reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation;   means for receiving a medium access control element (MAC CE) that indicates a beam failure on the primary sidelink carrier, the one or more secondary sidelink carriers, or both; and   means for transmitting, in response to receiving the MAC CE, an aperiodic reference signal on the primary sidelink carrier.   
     
     
         39 . An apparatus for wireless communication, comprising:
 means for transmitting reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation;   means for receiving a first medium access control element (MAC CE) that indicates a failure of a beam on a secondary sidelink carrier of the one or more secondary sidelink carriers;   means for transmitting, in response to receiving the first MAC CE, one or more aperiodic reference signals on other secondary sidelink carriers of the one or more secondary sidelink carriers;   means for receiving a message indicating one or more beams of the other secondary sidelink carriers that are viable; and   means for transmitting, via a second MAC CE on the primary sidelink carrier, a beam switch message based at least in part on the one or more beams that are viable.   
     
     
         40 . An apparatus for wireless communication, comprising:
 means for receiving reference signals on a primary sidelink carrier and on one or more secondary sidelink carriers using carrier aggregation;   means for detecting a beam failure based at least in part on measurement of the reference signals; and   means for transmitting a first aperiodic medium access control element (MAC CE) that indicates a failure of one or more beams on one or more of the primary sidelink carrier or the one or more secondary sidelink carriers.